Hitherto, dielectric resonant devices have been used as filters and the like used in microwave bands, each dielectric resonant device having a ceramic cavity which has an open face, contains a dielectric core, and is provided with a conductive film, the cavity being covered by a metallic panel at the open face thereof.
In particular, a dielectric resonant device is disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 9-51201 and 8-222905, in which a metallic panel provided with a coupling loop and the like formed thereon and having a coefficient of linear expansion substantially the same as that of a material for resonator is directly connected by soldering to an electrode formed on an open face of a ceramic cavity. Another dielectric resonant device is disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 8-181513 and 8-65017, in which an open face of a ceramic cavity is covered by a printed circuit board provided with a coupling loop and the like formed thereon, and a conductive film of the ceramic cavity and the printed circuit board are connected to each other by soldering via a grounding plate therebetween, or the grounding plate is screwed to the substrate side.
However, a problem has been found in the above dielectric resonant device disclosed in Japanese Unexamined Patent Application Publication Nos. 9-51201 and 8-222905, in that since the thermal capacity of the ceramic cavity is large when the dielectric resonant device is large, a large temperature gradient is likely to be generated when soldering and a stress is applied to the joint part, whereby cracks causing breakages are easily produced in the joint part during use for a long time. The dielectric resonant device disclosed in Japanese Unexamined Patent Application Publication Nos. 8-181513 and 8-65017 requires a plurality of the grounding plates, thereby increasing the number of components and increasing manufacturing costs as a whole.
There is a problem in either dielectric resonant device of above, in that the manufacturing efficiency significantly decreases when the shape of the open face of the ceramic cavity is complex. The tendency toward the decrease of the efficiency is remarkable particularly when a regulated lead-free solder is used.